Preheat oven to 200C. Place beetroot on a large piece of foil, scatter with thyme, drizzle with 30ml oil, fold into a parcel and roast until tender (15-20 minutes). Peel, halve, keep warm.
Meanwhile, cook potato in boiling salted water until tender (10-15 minutes), drain and keep warm.
Heat a large ovenproof frying pan over medium-high heat, add duck, skin-side down, cook until crisp (5-6 minutes), turn, and transfer to oven until warmed through (4-5 minutes). Coarsely shred meat from bones, add to potato with beans, frisée, parsley, beetroot, reserved beetroot leaves and mustard. Drizzle with vinegar and remaining oil, season to taste, toss to combine and serve immediately.